Method for adjusting the bath composition in a continuous electrodeposition process



G. E. F. BREWER ET AL v 3,355,373

STI ITION IN N PROCESS Nov. 28, 1967 METHOD FOR ADJU NG THE BATH COMPOS A CONTINUOUS ELECTRODEPOSITIO Filed Dec.

INVIENTORL` Byhmm "BW United States Patent Oliice 3,355,373 Patented Nov. 28, 1967 3,355,373 METHGD FOR ADJUS'IING THE BATH COMPGSI- TION iN A CONTINUGUS ELECTRODEPOSITIQN PRG-SESS George E. F. Brewer, Novi, and Gilbert L. Burnside, Oak

Park, Mich., assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Fiied Dec. 36, 1963, Ser. No. 334,333 6 Claims. (Cl. 2tl4-1S1) ABSTRACT F THE DISCLGSURE Method for adjusting the composition of an aqueous dispersion of organic coating material for use in electrodeposition coating or" electrically conductive workpieces comprising continuous electrodeposition of coating material from said dispersion upon an electrically conductive sheet material, monitoring the coating so obtained and adjusting the replenishment feed to said dispersion in accordance with changes in the coating formed on said sheet material. One preferred embodiment of this method comprises feeding such dispersion to a first bath in a tank in which electrically conductive workpieces are continuously coated by electrically induced deposition, feeding a small quantity of such dispersion to a second bath in a smaller tank, continuously passing a strip of electrically conductive sheet material through said second bath at a rate such that the ratio of the volume of said second bath to the surface area of said sheet material passing therethrough per unit time is significantly smaller than the ratio of the volume of said tirst bath to the surface area of the workpieces passing therethrough per unit time, electrodepositing coating material on said sheet material as it passes through said second bath, monitoring the coating electrodeposited on said sheet material from said second bath, and adjusting the replacement feed to said first bath in accordance with changes in the coating formed on said sheet material.

This invention relates to the coating of an electrically conductive object by electrically induced deposition of an electrically charged, relatively nonconductive or relatively nonionic coating material from a liquid bath. In particular, this invention is concerned with .continuous electrocoating processes wherein metallic objects are coated in an aqueous medium with an organic coating material dispersed therein. More particularly, this invention is concerned with methods and means for predicting the electrocoating process requirements for a given coating formulation and or predicting the performance of a given coating formulation with time in a continuous electrocoating process.

It is comparatively simple to formulate an electrocoating bath from which useable work pieces can be obtained at the outset of the coating process. It is considerably more difficult to formulate and maintain an electrocoating bath that will provide long term bath stability in a continuous operation. Aside from providing the desired coating quali ties the formulation per se must be stable with time under the conditions of coating and the relative concentrations of all dispersed components must be kept within the limits that will maintain such stability. The separate components of an electrocoating bath ordinarily do not deplete at a rate corresponding to their relative concentrations in the bath. Hence, one method for maintaining bath constancy is to employ a make-up feed in which the relative concentrations of components differ from those of the bath at coating initiation, i.e., by replenishing the components of the bath in accordance with their relative rates of depletion.

It is one object of this invention to provide efective method and means for predicting with a relatively small quantity of coating material the operational stability of a given coating formulation in a large scale continuous electrocoating operation.

lt is another object of this invention to provide effective method and means for reducing the time required to determine the effective life expectancy of a given coating formulation in a continuous electrocoating operation with replenishment of the various bath components at an optimum rate.

It is another lobject of this invention to provide effective method and means for determining for a given coating formulation the most effective rate of replenishment for the several components thereof.

It is another object of this invention to provide effective method and means for periodic monitoring of a large scale electrocoating operation using relatively small quantities of the production bath to detect compositional changes in such bath in time to compensate for such changes before the imbalance reaches the stage within the production bath Where product quality is significantly affected.

It is still another object of this invention to provide effective method and means for predicting with a relatively small amount of a given coating formulation the amount of electrical energy required for an electrocoating operation of given size employing such formulation.

With the foregoing and other objects in View, as will hereinafter become apparent, this invention comprises the methods, combinations, construction and arrangement of parts hereinafter described and/or illustrated in the ac companying drawing wherein:

FIGURE l is a partially schematic, partially sectional side view of one embodiment of the device of this invention, and

FIGURE 2 is a perspective view of a strip of coil stock adapted for use with the device of FIGURE l.

Referring now to FIGURE l, a power supply unit 11 is shown in electrical connection with motor 13 which, through a conventional belt and pulley arrangement, drives sprocket wheels 15 and 17 positioned above opposite sides of substantially U-shaped coating tank 19 at adjustable but synchronized peripheral speeds. One terminal of power unit 11 is in electrical connection with tank 19 and secondary electrode 21 within tank 19. Except for the electrical connections with power unit 11, tank 19 and electrode 21 are insulated from the rest of the system and may be insulated from each other. A second terminal of power unit 11 is in electrical connection with the coil stock 23 0f roll 25 and with ground.

Power unit 11 is constructed and arranged to receive electrical energy from a conventional alternating current power source, and through conventional rectiers to convert such energy to a direct current or its equivalent. Power unit 11 ordinarily is designed to provide the system with a direct current adjustable in the range of O to of the aforementioned resins `2 square feet since to 500 volts or greater. Motor unit 11, as here shown, or

90 amperes orV greater and 0 13 may receive its power from from an independent source.

When the device here shown is in operation tank 19 containe an aqueous electrocoating bath 29 supplied at a predetermined rate from paint feed tank 31 via conduit 33, pump 35 and conduit 37. Pump 35 is actuated by conventional power means not shown. In one embodiment this bath is continuously recycled to feed tank 31 via conduit 39. Feed tank 31 is provided with agitation means 41 and is in turn supplied from paint supply source 49 via conduit 43, pump 45 and conduit 47. Pump 45 is actuated by conventional power means, not shown.

Organic coating Vmaterials which may be used in an electrocoating bath include, but not by way of limitation, alkyd resins, acrylate resins, epoxy resins, phenolformaldehyde resins and various other organic resins or mixtures of the foregoing with each other or other filmforming materials including binding agents and extenders conventionally employed with water based paints. Such materials may include or be employed with other organic monomers and/ or polymers including, but not by way of limitation, hydrocarbons and oxygen substituted hydrocarbons such as ethylene glycol, propylene glycol, glycerol, various monohydric alcohols and various carboxylic acids, ethers, aldehydes and ketones. The film-forming material may include or be employed withpigments, metallic particles, dyes, drying oils, etc., and may be dispersed as a colloid, emulsion or emulsoid. Coating materials adapted for anodic deposition may include one or more of the aforementioned resins having free carboxyl Uroups or other suitable acid or acid forming groups in their polymeric structure. Dispersion of these resins in water can be effected by the addition of a suitably basic material such as ammonia, water soluble amines, mixtures of polymeric and water soluble amines etc. Coating materials adapted for cathodic deposition may include one or more having amine or substituted amine groups, eg. quaternary ammonium groups, in their resin structure. Dispersion of the latter resins can be effected by the addition of suitably acidic materials such as water soluble carboxylic acids, eig., acetic acid, propionic acid, etc., and suitably buffered forms of certain inorganic acids, eg., phosphoric.

The volume to surface ratio with respect to operational volume of tank 19, i.e., the volume of bath 29, and coil stock 23 is considerably lower than the corresponding relationship in a production unit and preferably in the range of about 2-5 to l gal./sq. ft. This ratio may be varied with the specic embodiment. Typically, a segment of coil stock 1 foot square, i.e., a totalsurface area of about both sides are immersed, would be in residence Vin a -gallon bath. In one embodiment a U-shaped member 19-1 is positioned within tank 19 as indicated in broken outline in FIGURE l.

In the illustrated embodiment the device is threaded by drawing a strip of coil stock from roll 25, under guide roll 51, over sprocket wheel 17, between sprocket wheel 17 and guide roll 53, through tank 19, over sprocket wheel 15, under guide roll 55, over drip tank 57, under guide roll 59, over payout sprocket wheel 61 and to a receiving means here indicated by roll 63 which may also be belt driven in synchronization with the aforementioned sprocket wheels by means not shown. In this embodiment the coil strip 23 is slotted as shown in FIGURE 2 to provide engaging means for the teeth of sprocket wheels 15, 17 and 61. Sprocket wheel 61 is interconnected with sprocket via a conventional belt and pulley arrangement and is driven by the turning of sprocket wheel 15 Which in turn is driven by motor 13.

Coil stock 23 is a flexible metal strip the surface of which has been cleaned, sanded, chemically treated etc., in the same manner as the surfaces of the intended workpieces for the production unit. In this embodiment coil stock 23 is positioned on sprocket wheels 15 and 17 so formic acid,

as to leave a substantially U-shaped loop which extends into the coating bath 29 and substantially conforms tothe U-shaped cross sectional contour of tank 19. IIn this man- Vner `there is maintained a small but definite spacing between the outer side of the flexible coil stock 23 and the wall of tank 19.

In this embodiment guide roll 55 serves to direct the motion of the coil stoc-k 23 below the highest point to which the coil stock rises when leaving the bath. Thus means are provided to prevent bath uid carried from the bath by the rising strip to flow back into the bath after it reaches a predetermined point. v

Tank 19 is also in fluid communication with a plurality of bath control means. In this embodiment such control means include a temperature control unit 101, an ion exchange type filtration unit 201 and a dialysis type filtration unit 301. n

Temperature control unit tinuously controlling the coating bath temperature through either heating or cooling. moved from coating tank 19 via conduit 103. It is passed via pump 105, driven Vby power means not shown, through a heat exchanger 107 and returned to tank 19 via conduit 109, valve 111 and conduit 113. Heat exchanger iiud, eg., transformer oil, is passed from a heater and refrigeration unit through conduit 117, through heat exchange unit 107Y and returned to heater and refrigeration Y unit 115 via conduit 112. Inside heat exchanger 107' the bath fluid and the heat exchange iluid pass in heat exchange relationship with each other through adjacent conduits. In this mode of operation above described valve 111 is open. The heat exchange unit illustrated provides one form of external heat exchange. It is within the scope of this invention to control the bath temperature through use of an internal heat exchanger. t

An ion exchange unit 201 may be brought into the operation by opening valve 205 and closing valve 111. When valve 111 is closed and valve 205 is open the bath uid leaving heat exchange unit 107 via conduit 109 is passed via conduit 203, valve 205, conduit 207, ion exchange tank 209 and conduit 211 into conduit 113 through which it is Y K change material comprises an organic carboxylic or sulfonic acid comprising resin. Removal through ion exchange means is essentially limited to the removal of ionic or electrically Vcharged materials. It is often desirable to remove bath components,

eg., deterioration products etc., on the basis of size. For

this purpose a dialysis unit 301 is provided. This Vunit is Y brought into the operation by continuously removing bath liquid from tank 19 via conduit 303 and passing it via pump 305 and conduit 307 through dialysis unit 309 from whence it is recycled to tank 19 via conduit 311. Pump 305 is Ypowered by conventional means not shown. Dialysis unit 309 is a conventional compartmentalized dialysis unit the compartments of which are separated by membraneous or porous walls or diaphragms which admit the escape of particles of less than a predetermined maximum size. Such particles escape into water compartments adjacent thereto which are supplied with water via conduit 313 and evacuated via conduit 315.

In the illustrated embodiment the coil stock is indicated to be positive and grounded While the tank 19 and electrode 21, when the latter is used, are negatively charged. It is within the scope of this invention to change or reverse the electrical condition of these components in any 101 provides means for con# Bath fluid is continuously re-V manner compatible with the electrocoating operation being tested. A counter 71 is actuated by the belt drive means between motor 13 and sprocket wheel 15 to provide a record of the length of coil stock passing through the bath.

In another embodiment a plurality of supply rolls similar to roll 25 are positioned in line and the coil stock drawn therefrom is passed through a laterally extended bath as parallel bands which can be alternately lifted from the bath and submerged into the bath.

In another embodiment one or more segmented coil strips are employed in lieu of the continuous strip employed in the illustrated embodiment. In this embodiment alternating conductive and nonconductive segments are passed through the bath with the conductive segments making contact with an electrode of proper polarity while in Contact with the bath.

It is within the scope of the foregoing embodiments t provide a plurality of electrodes and associated electrical components for applying different voltages to different electrodes in contact with the bath and for providing a workpiece passing through the bath with a reversal of polarity in the course of such passing.

In other embodiments control units, which advantageously are positioned in conduit 39, provide means to continuously measure and record the density, viscosity, conductivity, surface tension and pH of the bath.

The invention will be more fully understood from the following examples which are illustrative of the several operational embodiments thereof and are not to be considered as limitations upon the scope of invention as set forth in the claims.

EXAMPLE I An electrocoating bath of approximately gallons of which 7.25% was non-volatile material was prepared by dispersing gallon red primer (a carboxylic acid resin and iron oxide pigment) in 4% gallons of water and 200 ml. of concentrated ammonia.

Electrocoating was carried out using this formulation at 85 F., 200 volts, and 5.0 amperes. The coating operation Was carried out using apparatus correspondingV to that shown in FIGURE l of the drawing. The coil stock employed was 12 inches wide. The continuous coating was carried out with 12 inches of Athe strip submerged in bath while the strip was passed through the bath at the rate of l2 inches per minute. In this operation a workpiece was in electrical connection with ground and was positive with respect to the coating tank. Downstream from the bath segments of the coated strip were clipped at 1/2 hour intervals and finished in the conventional manner, i.e., by rinsing, baking, etc. The coatings on the clipped segments were measured and found to have an average thickness of about 1.0 mili0.1 mil.

The addition of about 1/2 ounce of the aforementioned primer per minute maintained the aforementioned concentration of solids while the water content of the bath was held constant by replacement in accordance with use. A total of 1,910 lineal feet of coil stock was passed through the bath in accordance with the foregoing procedure. Coating was terminated when string-like coagu- Iations formed in the bath and marred the appearance of the finished film. This bath formulation was found to permit the coatingof about 435 sq. ft. of metal per gallon of paint added to the bath.

Taking into consideration the above described deterioration of this bath, the effective use of this formulation is reduced by the resulting discard to about 400 sq. ft per gallon.

EXAMPLE II A second electrocoating bath was prepared from 32/3 quarts of black primer and 161/3 quarts of tap water containing a water soluble amine. The coating was carried out in the same manner aforedescribed in Example I. A 0.7 mil coating was produced on the coil stock using 150 volts and 5.4 amperes at F. In the course of coating 410 sq. ft. of coil stock, 31/2 quarts of the primer were added to maintain the bath solids at a constant concentration. At this time pinholes began to appear in the coating. Thus, addition of each gallon of this primer would provide for the coating of 470 sq. ft. of surface. The loss from bath dumping -would reduce the a'ective coverage of this formulation to about 230 sq. ft. per gallon of paint using the apparatus aforedescribed.

To determine the stability life of this formulation in a larger scale operation, a production size bath Was charged with 660 gallons of the primer and about 3,000 gallons of water. Coating was carried out under essentially the same conditions used with the S-gallon operation. About 600 gallons of primer were added to maintain a constant bath composition and about 210,000 sq. ft. of metal were coated when similar pinholes began to appear in the coating. Thus, bath failure in both the 5-gallon coil stock bath and the 3,600 gallon product-ion bath resulted at slightly above of one complete turnover of solids.

EXAMPLE III A third electrocoating formulation was prepared using l gallon of a similar but different primer and 4 gallons of water. The coating process was carried out as in the previous examples except that a 0.9 -mil coating was produced at 225 volts, l1 amperes, and 110 F. A total of 2.4 gallons of primer were added while 1,170 sq. ft. of coil stock were being coated. A peculiar incompatibility of resinous materials was then evidenced by large discolored spots in the coating. Examples of the discolored coatings and the coatings made prior to this form of bath failure were subjected to sait spray tests after finishing. These tests showed a gradual decline in salt spray resistance from the time the iirst coatings were made through the time of bath failure. Chemical analysis of the deteriorated coating bath revealed that the replacement primer was deficient in one of the components of the original bath. This deficiency was restored and the coatings made thereafter revealed that the appearance and durability of the film were restored thereby.

EXAMPLE IV A 3,600 gallon electrocoating bath was prepared employing the formulation of Example II and coating was carried out in a production type tank through which automobile wheels were passed While suspended from an overhead conveyor. In the larger tank about sq. ft. of steel surface were coated per minute at a constant current of about 330 amperes. A S-gallon bath of the same formulation was placed in the aforedescribed apparatus of this invention. A series of tests were conducted with both the S-gallon and 3,600-gallon tanks. In the two operations the current draw was found to be affected by the total workpiece surface area submerged at any given time and by the workpiece surface area entering per: unit time. Otherwise stated the current required is the sum of the current owing between the workpiece surface area within the bath and the electrode or electrodes of opposite polarity plus the current requirements determined' by the rate at which workpiece area is introduced into the bath.

A test was carried out in which the current ow of a coating operation in the apparatus of this invention using a S-gallon bath was determined. The movement of the strip of coil stock through the bath was then stopped and the current flow was again determined. The second reading was employed to compute the amperage per sq. ft. of workpiece residing in the bath. The difference between the rst and second readings was used to compute the current requirement per sq. ft. of material introduced into the bath per minute. Several such tests were conducted using the coating formulation of Example II. The results of these tests are set forth in the following table.

Of.) l'

new surface entry into bath IMI- Rate of Run, Submergcd Area, Area in Sq. Ft.

inch/Min. Sq. Ft. Introduced Amp Observed Per Min.

6 1 1 2. 5 1 0 0. "i0 9 1. 5 1. 5 3. G 0 l. 5 0 (l. 8' 12 2. 0 2. 0 4. 9 0 2. 0 0 1. 1 15 2. 5 2. 5 6. 6 0 2. 5 O 1. 4

Thus,l the current requirement of this bath was deterined to be about 0.56 amp/sq. ft. for the workpiece area within the bath plus about 2.0 amp/sq. ft. of workpiece surface entering the bath per minute.

Using this determination the current' requirements of the 3,600-gallon bath operation were predicted as follows:

Table II.-C0mpuat0n of current requirements of pro- Amp/Sq. Ft.

.Amp/Sq. Ft.

submerged Introduced Per Min.

duction size bath with observed requirements of coil Y coater 4from Table I Amperes @0.56 yamp/sq. ft. 112. @2.0 amp/sq. it. 210

Computed current ow 322 Observed current ow a 330 EXAMPLE V A continuous electrocoating operation is carried out wherein an electrically conductive strip is provided with an organic coating by electrically induced deposition in accordance with the procedures of the preceding example and with the additional step that the pH of the coating bath is continuously measured and recorded.

EXAMPLE VI A continuous electrocoating operation is carried out wherein an electrically conductive strip is provided with an organic coating by electrically induced deposition in accordance with the procedures of the preceding example and with the additional step that the density ofthe coating bath is continuously measured and recorded.

EXAMPLE VH A continuous electrocoating operation is carried out wherein an electrically conductive strip is provided with an organic coating by electrically induced deposition in accordance with the procedures of the preceding example and with the additional step that the viscosity of the coating bath is continuously measured and recorded.

EXAMPLE VH1 A continuous electrocoating operation is carried out wherein an electrically conductive strip is provided with an organic coating by electrically induced deposition in accordance with the procedures of the preceding example and with the additional step that the conductivity of the coating bath is continuously measured and recorded.

The terms nonconductive coating material and relatively nonconductive coating material as employed herein refer to 4a substance having a specific electrical resistance above that of the coating bath in which it. is dispersed and above about 50G-ohm centimeters at 75 vF.

VHaving described certain embodiments of the invention in detail it will be understood that various changes and modications can be made in the method and the appa'- ratus employed to carry out the method without departing from the spirit and scope of the invention, as defined in the claims.

We claim:

. In a method of operating a continuous electrocoating workpiece area:

submerged 200 sq. ft. Entering 195 sq. ft./min.

5 bath therein, passing a continuous strip of electrically conoperation wherein electrically conductive objects are provided with an organic coating by electrically induced depositionof organic coating material upon said objects while said objects are passing through an aqueous dispersion ofjsaid coating material retained in a coating tank, the improvement. which comprises feeding a iirst portion of an aqueous dispersion of organic coating material to said tank to provide arst bath therein, feeding alsecond and significantly smaller portion of said dispersionkto a second and significantly smaller tank to form a second ductive sheetmaterial through said second bath at a rate such that the ratio of the volume of said second bath to the surface area of said strip passingI therethrough per unit time is significantly smaller than the ratio of the volurne of said rst bath to the surface area of 'the work# pieces passing therethrough. per unit time, transmitting a direct current of electrical energy through said second bath Vbetween the segment of said strip-within said second bath and an electrode in contact with said second bath thereby forming an organic coating on the coating on said strip and adjusting the replacement feed to said first bath in accordance with changes in the coating formed on said strip.

ZJIn a method of operating a continuous electrocoating operation wherein electrically conductive objects are provided withan organic coating by electrically induced deposition of organic coating material upon said objects While-said objects are passing through a coating bath comprisingan aqueous dispersi-on of said organic coating material vretained in a coating tank, the improvement which comprises removing a portion of said bath, forming a second bath consisting of said portion, passing a continuous strip of electrically'conductivc sheet material' through said second bath at a rate such that therratioY of the volume of said second bath to the surface area of said strip passing therethrough perrunit time is significantly smaller than the ratio ofthe volume of said tirst bath to the surface area ofthe workpieces passing therethrough per unit time, transmitting a direct current of electrical energyV through said second bath between the segment of said strip within said second bath and au elect-rode in contact with saidr vided with an organic coating by electrically induced Y deposition of organicrco'ating material upon said objects While said objects are passing sion of said coating material retained in a coating tank, the improvement which comprises feeding a first portion of an aqueous dispersion of organic coating material to said tank to provide a first bath therein, feeding a second and signicantly smaller portion of said dispersion to a second and significantly smaller tank to form a second bath therein, passing a continuous strip of electrically conductive sheet material through said second bath in a manner such that the volume of said second bath is about 2 to said strip, monitoring i through an aqueous disperg about gallons per each square foot of surface area of said strip in residence therein, transmitting a direct current ow of electric energy through said second bath between the segment of said strip therein and an electrode in contact with said second bath thereby forming an organic coating on said stn'p, monitoring the coating on said strip and adjusting the replacement feed to said first bath in accordance with changes in the coating formed on said strip.

4. In a method of operating a continuous electrocoating operation wherein electrically conductive objects are provided with an organic coating by electrically induced deposition of organic coating material upon said objects while said objects are passing through a coating bath comprising an aqueous dispersion of said organic coating material retained in a coating tank, the improvement which comprises removing a portion of said bath, forming a second bath consisting of said portion, passing a continuous strip of electrically conductive sheet material through said second bath in a manner such that the volume of said second bath is about 2 to about 5 gallons per each square foot of surface area of said strip in residence therein, transmitting a direct current ow of electrical energy through said second bath between the segment of said strip therein and an electrode in contact with said second bath thereby forming an organic coating on said strip, monitoring the coating on said strip and adjusting the replacement feed to said first bath in accordance with changes in the coating formed on said strip.

5. A method for adjusting the coating properties of an electrodepositable organic coating material in electrically induced deposition from an aqueous dispersion thereof which comprises forming a coating bath comprising an aqueous dispersion of said coating material, continuously passing a strip of sheet material at least a portion of which is electrically conductive at a predetermined rate through said bath, providing a direct current of electrical energy through said bath between an electrically conductive segment of said strip passing through said bath and an electrode in Contact with said bath and spaced apart from said strip and electrodepositing a coating of said 10 organic coating material upon said strip as said strip passes through said bath, monitoring the coating thus formed upon said strip and adjusting the replacement feed to said bath in accordance with changes in the coating formed on said strip.

6. A method for adjusting the coating properties of an electrodepositable organic coating material in electrically induced deposition from an aqueous dispersion thereof which comprises forming a coating bath comprising an aqueous dispersion of a Water-soluble amine and an organic resin having free carboxyl groups thereon, continuously passing a strip of sheet material at least a portion of which is electrically conductive at a predetermined rate through said bath, providing a direct current of electrical energy through said bath between an electrically conductive segment of said strip passing through said bath and an electrode in contact with said bath and spaced apart from said strip and electrodepositing a coating of said organic resin material upon said strip as said strip passes through said bath, monitoring the coating thus formed upon said strip and adjusting the replacement feed to said bath in accordance with changes in the coating formed on said strip.

References Cited UNITED STATES PATENTS 1,589,329 6/ 1926 Sheppard et al 204-183 2,576,362 11/1951 Rimbach 204-181 2,793,345 5/ 1957 Hags 118-6 3,093,511 6/ 1963 Weisel et al. 204-181 3,172,779 3/ 1965 Warshaw et al. 118-9 OTHER REFERENCES Electroplating Engineering Handbook, 2nd ed., edited by Graham, Reinhold Publishing Corp., 1962, pp. 329 and 330.

ROBERT K. MIHALEK, Primary Examiner. JOHN H. MACK, Examiner. E. ZAGARELLA, Assistant Examiner. 

1. IN A METHOD OF OPERATING A CONTINUOUS ELECTROCOATING OPERATION WHEREIN ELECTRICALLY CONDUCTIVE OBJECTS ARE PROVIDED WITH AN ORGANIC COATING BY ELELCTRICALLY INDUCED DEPOSITION OF ORGAINIC COATING MEATERIAL UPON SAID OBJECTS WHILE SAID OBJECTS ARE PASSING THROUGH AN AQUEOUS DISPERSION OF SAID COATING MATERIAL RETAINED IN A COATIN GTANK, THE IMPROVEMENT WHICH COMPRISES FEEDIN G A FIRST PORTION OF AN AQUEOUS DISPERSION OF ORGANIC COATING MATERIAL TO SAID TANK TO PROVIDE A FIRST BATH THEREIN, FEEDIN A SECOND AND SIGNIFICANTLY SMALLER PORTION OF SAID DISPERSION TO A SECOND AND SIGNIFICANTLY SMALLER TANK TO FORM A SECOND BATH THEREIN, PASSING A CONTINUOUS STRIP OF ELECTRICALLY CONDUCTIVE SHEET MATERIAL THROUGH SAID SECOND BATH AT A RATE SUCH TAHT THE RATIO OF THE VOLUME OF SAID SECOND BATH TO THE SURFACE AREA OF SAID STRIP PASSING THERETHROUGH PER UNIT TIME IS SIGNIFICANTLY SMALLER THANTHE RATIO OF THE VOLUME OF SAID FIRST BATH TO THE SURFACE AREA OF THE WORKPIECES PASSING THERETHROUGH PER UNIT TIME, TRANSMITTING A DIRECT CURRENT OF ELECTRICAL ENERGY THROUGH SAID SECOND BATH BETWEEN THE SEGMENT OF SAID STRIP WITHIN SAID SECOND BATH 